Gas discharge lamps and incandescent lamps are well known in the art. Gas sources and incandescent lamps have relatively high energy consumption. Further, gas sources and incandescent lamps have relatively short lifetimes and are susceptible to breakage, typically leading to high maintenance costs. Further, the light intensity of gas discharge lamps tends to decrease over time with use. Additionally, gas discharge lamps produce ozone due the hazardous material/gas they require for excitation of electrons. After a gas discharge lamp's useful life, hazardous material and poisonous gases used in the lamp are released to environment affecting, among other things, the ozone layer. Additionally, gas discharge lamps produce ultra violet light that tends to cause deterioration of many materials, damage to some living organisms, and to some elements of the environment.
Solid state lighting, such as light emitting diode (LED) lighting has been developed to overcome some of the problems of gas discharge lamps and incandescent lamps. Many conventional LED devices, however, are limited by thermal energy-management issues.
It is known that LEDs exhibit negative temperature coefficient aspects, i.e. at fixed power input, as the device's operating heat rises, the device's light output decreases and it shortens the life of LED. It is, however, desirable to run LEDs using high current, because the higher the current, the higher the brightness of the emitted light. Further, high heat during use can shorten the useful life of an LED. Accordingly, there is motivation to remove heat as much as possible in order to operate an LED optimally with regard to power input and light output and LED life.
In addition, where a plurality of LED's are required for higher brightness, there are limits in conventional lamp technology to the number of LEDs within a defined space due to the problem of heat dissipation. Accordingly, it is desirable to cool an LED device in order to maximize energy efficiency and lifespan as well as to broaden design options.
Conventional solutions to undesirable thermal buildup include fans, cooling fins, spacing assemblies, etc. to reduce lamp housing temperature. Another conventional solution involves mounting LED modules on large conductive heat sinks. A light emitting diode (LED) must be mounted on a relatively large metal heat sink to dissipate the heat when the diode is run using high current. In high use and in demanding situations, the thermal transfer from the LEDs through a thermally connected conventional heat spreading plate to the housing is insufficient to maintain a desirable LED temperature. Unfortunately, thermal back-flow may occur as a lamp housing is heated by the ambient atmosphere beyond an optimal point which allows thermal conduction back to the heat spreading plate. In such situations, rapid LED degradation often occurs and unit efficiency drops.
Solid state thermoelectric modules (TEM), also referred to as thermoelectric coolers (TEC), or heat pumps, have been used in various applications. A TEM, in a thermocooling application, converts electrical energy into a temperature gradient, known as the “Peltier” effect. By applying a current through a TEM, a temperature gradient is created and heat is transferred from one side, the “cold” side of the TEM to the other side, the “hot” side.
The Peltier effect is well known by those skilled in the related arts and provides an active solid-state thermoelectric cooling function from a cool side to a hot side. The cool side is commonly placed against a surface or substrate which requires cooling. For example, the back surface of an LED assembly. The hot side is commonly placed against a surface or substrate which absorbs the transferred thermal energy and transfers it through conduction to a heat spreading plate. Through the utilization of these thermo-electric effects, thermal transfer from a cool side to a hot side can be controlled by controlling a current supplied to the thermo-electric effect.
Many conventional solid-state lamps are expensive to manufacture, and, due to the nature of the failures in a solid-state lamp, difficult and expensive to repair. Nevertheless, the energy-efficiency characteristics of solid-state lamps make them an attractive alternative to incandescent and fluorescent lighting.
For the foregoing reasons, there is a need for a solid-state lamp having effective thermal management with improved maintenance qualities.